This is an open-label study to evaluate the safety, tolerance, and pharmacokinetic parameters of both oral and intravenous administration of fluconazole in pediatrics oncology patients. This study will enroll children 15 years of age and younger and give them fluconazole at three dosage levels either orally or intravenously for one week. 6 patients will be entered at each dosage and administration subgroup. Each patient will have multiple plasma samples obtained to evaluate for both toxicity and pharmacokinetics. A high performance liquid chromatographic method will be used in the determination of plasma fluconazole concentrations.